Scale Soaring UK

In the North of England, we call it Sod's Law - if it can go wrong it will.

Yesterday evening was a good demonstration of this.

It was a perfect balmy evening and after tea on the patio I decided to have a quick fly of my 4m ASH25 off the field next to our house.

I checked my 5 cell NiMh receiver battery (...I bet you know where this is heading already!) and it read a healthy 5.9V. There was obviously plenty of charge left in it after my hour flying on Sunday, so nothing to worry about there.

I paused briefly to consider connecting a second receiver battery but thought what's the point, I'll only be flying for maybe 30 mins before sunset.

I also picked up my vario module, then hesitated - was I becoming too dependent on this for finding lift? Was it eroding my (already rubbish) thermal-hunting skills? I popped it back on the bench. This flight would be au naturel.

And what a beautiful flight it was, the air as silky smooth as a flight simulator, the lift everywhere, the light golden. I'd only needed a 20 second motor run to get into the lift and then I was amidst the circling buzzards. Who needs a vario, I scoffed to myself.

Time slipped by, the way it does when you are utterly absorbed in the simple thrills of piloting a silent sailplane around a blue sky flecked with golden clouds.

And then that uneasy feeling that your little white crucifix of a model is not quite responding as you expected to your controls.

You give it some deliberate control inputs, to see if you can coax it back into controlled flight.

But then that growing, sickening feeling in the pit of your stomach that it has broken away from your radio wave. Maybe it's just a momentary blip, you reason, with a surge of optimism. But then the confirmation, as you stir your thumbs wildly, flick every switch on your transmitter, joust the aerial above your head in a jaunty fashion, that you are no longer piloting this plane.

By now the model was past the edge of our field and heading for the woods, but still circling upwards, managing rather well without my control inputs, thank you very much. I stood for a few seconds, pondering that THIS is what free-flight modellers consider fun.

The model cleared the top of the ridge and disappeared out of sight, heading towards...the lake.

We've lived here 20 years and the lake has been such a lovely constant in our lives. Taking our toddlers to see it in Spring, surrounded by bluebell-speckled woodland, teaching our 10 year-olds to skim stones across its smooth Summer waters, skating with our teenagers on its frozen wintry crust. But always, at the back of my mind, I knew that one day it would claim a model.

Realising that the model could, at this moment, be splashing down into its murky green waters, and that the race between gravity and buoyancy may already have started, I galloped back to the house, calling for my kids to join the rescue in a voice that I hoped would impart urgency, but not reveal the full extent of my panic. It's one thing crashing your toy plane, but you want to cling onto a shred of dignity in your kid's eyes, don't you?

We made a search plan. It was simple. The model must be somewhere within about a 500m x 500m area. We simply needed to find it. Unfortunately, about 90% of this area was covered by the lake. So we needed to find it quickly.

As we jogged into the woods towards the lake, I wondered if I'd prefer it to have landed in the woodland, or the (statistically much more likely) lake.
In other words, did we fancy swimming or tree-climbing?

Arriving at the lake, we split up, like they do in movies. Except that in movies, 2 of the search party is seldom clothed in pyjamas and flip flops (I obviously hadn't adequately explained to the girls that they would be bush-whacking through dense undergrowth, climbing trees, and possibly swimming in the leech-laden waters of the lake.)

I criss-crossed the wooded ridge while the girls took paths around each side of the lake. In no time I was sweat-stained and wheezing, but reached a clearing where I could see the entire lake below. Not a trace of the model. Not a ripple disturbing the surface except for two plucky swimmers enjoying the cool waters below, and possibly feeding a few leeches in the process. I ached to see a flash of shiny white Profilm or a red wingtip poking, excalibur-like, from the waters. But nothing. Silence. Only the flip-flapping of my kids jogging along the water's edge.

As I made my way back down to the lake, I'd started to come to terms with my loss. Get it into perspective. Put it right at one end of the scale of life's little losses. "They all end up in bin-bags" as my dad sagely commented many times throughout my childhood of aeromodelling. And then one of my kids called - they'd found it! Or rather one of the swimmers had seen it spiralling downwards over the lake, and crashing, un-B****y-believably, into a tree on the very water's edge - literally 4 feet from the lake. I was delirious with joy. Why is it that going home with bits is so much better than going home empty-handed?

The attached image shows the approximate path of the model from the field on the top right where we fly to the "landing" spot on the lake edge.

I think I'll draw a veil over the details of how we retrieved it from the tree, because, frankly, my main contribution was to entertain my kids by falling spectacularly through a tree after I discovered that one of the rotten branches couldn't support my bulky frame. Meanwhile my kids threaded themselves up through the tree, reached the stricken soarer, and passed the bits back to me.

Well as of course you know, it was the receiver battery. One of the cells had failed and the receiver found it couldn't do any receiving on just 3.6V.

If only I'd checked the date on the battery and noticed it was 2012 - and therefore due for recycling at the local tip rather than plugging into my plane.
If only I'd plugged in that second battery to the receiver (my usual policy on any plane over 5kg).
If only I'd landed after my planned half an hour, instead of greedily grabbing over an hour.
If only I'd fitted the vario so that I could have enjoyed regular battery voltage updates from the lady with the German accent.

So - Murphy's Law. If something can go wrong, it will.

I feel stupid because whichever way you look at it this was entirely my own fault, but it's one of those humbling reminders never to take chances. It's an open invitation to Mr Murphy.

Rog

P.S. Surveying the wreckage this morning, it's definitely a fixer-upper. The wings are almost unscathed and the front of the fuselage that I molded last Summer escaped with a few scratches. I'll just mold another rear fuselage. It's all part of the hobby.

I enjoyed reading that in a macabre sort of way, if only indeed and a salutary reminder to us all.

I must be lucky though, all my tree/foliage interactions have so far been entirely down to pilot error!

Sorry to hear about the demise of your model, but very brave of you to admit your failings. We have all been there at one point or another.
I still have models powered by Nimhs but none of the packs are more than 3 years old and they get cycled every six months or so. I also check them thoroughly during the annual CofA in December/ January.
Better luck next time!
Brian.

Roger,
NIMH- Yuk! These are for TV controls. Also, I am of the two batteries are better than one, line of thinking. You cannot get much electricity out of the chunk of lead in the nose.

Sad to hear of the loss of radio contact with your model , must admit never a fan of Nimb,s , false peaks when charging and a relatively high failure rate . Much , much prefer two LiFe batteries , a much better charge , no false peaks and a lower internal resistance .
They seem to have a long life , just don't let them discharge too low .
Good luck with the repairs . Ian Turney-White

John Mcnamara wrote: ↑19 Aug 2021, 16:22 You cannot get much electricity out of the chunk of lead in the nose.

Got to say John, the science teacher in me is itching to point out you can get a heap of electricity by adding a little sulphuric acid, but nobody likes a smarty pants!

Yes I agree switching from NimH to LiFe makes sense and I changed all my models over before the Leek event. So far I am very impressed. I have twin LiFe batteries in each plane with simple diodes per Robbie’s wiring diagram in the Equipment section. I notice they deliver their current with very little voltage drop; my cells gave 6.67V off the charger and after 3 hours flying still read 6.63V. At some point I’ll test them on the ground to find the voltage at which they start to drop off steeply, then I can set alarm limits comfortably above that level.

Ian,
Thanks also for your comments. I didn’t know about the low internal resistance or the need to avoid high discharge. I’ll give them an easy ride while I learn their characteristics.

Thanks again folks.
Rog

Roger, As you say, the discharge curve of a LiFe battery is very flat & it seems to be very difficult to use voltage as a means of detecting capacity remain.
As shown by a sample graph, the voltage appears to vary more due to load than capacity.
Peter

Cheers Peter. That’s exactly the info I was after.

So as suspected, voltage fall is a poor indicator of remaining charge for LiFe chemistry. I can see I’ll have to get myself a system to track the charge-state of each battery.

Thanks again Peter - you are a handy bloke to know!
Rog

Re the remaining capacity of a LiFe battery , I like to add up how long I have used /flown a model during a long session on freshly charged batteries and
when back home recharge them on a charger that shows how much current has gone into the battery to fully recharge it.
For example say you have flown for 90 minutes and you needed about 900 milliamps to fully charge your batteries , then you consume about 100 milliamps say for a 10 minute flight or 600 milliamps for 60 minutes flying or 900 milliamps for 90 minutes
If you apply a safe discharge of two thirds of the batteries capacity , say 2700 milliamp capacity battery reduced to 1800 milliamp which would give you about 180 minutes /2 hours flying . The timer on your transmitter can give you info on how long its been on/model flying.
Sorry its not super scientific but the above does seem to work and avoids running out of power .
I use a small note book for my models and note the info for each model including discharge rate .
Most models require lead ballast and I am a big fan of using a larger battery needing less lead , sound investment !
As others have said , with a flat discharge rate that drops off rapidly when nearly discharged , its more difficult to monitor your batteries based on voltage . Whatever , may your batteries support your model .
Ian Turney-White

Good idea to use recharge capacity to check what has been taken out of the battery
Also probably an idea to also periodically check the overall capacity to make sure you have an indication of what is being left in the pack (as pack capacity drops over time) before recharge.
Peter

Guru of all things OpenTx and its use in gliding, Mike Shellim, has a blog post on timing / LiFe battery use via the Tx:

http://rc-soar.blogspot.com/2016/09/usi ... fe_94.html

Roger

Sorry to hear of your incident, we have all had challenges of our own making one time or other. I remember once forgetting to connect an elevator ........

On the subject of batteries. I have never been persuaded by the LiFe approach, as it needs a lot of care, or programming to be safe. My approach to anything that is special / expensive, where it will fit, is now 2 packs of 2s li-on with an electronic switch, normally Emcotec, low cost v the £s flying with simple charging and monitoring v voltage in the pack which just leaves the dummy onethe sticks to worry about!

Regards
Chris